) where
import Control.Monad.State
-import Data.Bits (shiftL, (.&.), (.|.))
+import Data.Bits (shiftL, shiftR, (.&.))
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy as BL
-import Data.Char (ord)
import Data.Digest.Adler32 (adler32)
import qualified Data.Map as M
import Data.Word (Word8, Word32)
type Md4digest = BS.ByteString
type Adler32checksum = Word32
+type Checksum = (Word32, Int, Int)
+
type Signature = (Md4digest, Adler32checksum, Int)
fileSignatures :: BL.ByteString -> Integer -> [Signature]
genInstructions :: [Signature] -> Integer -> BL.ByteString -> [Instruction]
genInstructions f0sigs blockSize fnew =
- evalState (go fnew) 0
+ evalState (go 0 fnew) sig0
where
- go :: BL.ByteString -> State Word32 [Instruction]
- go fnew | fnew == BL.empty = return []
- | otherwise =
- let (blk, blks) = BL.splitAt (fromIntegral blockSize) fnew
- adlerSum = weakSig blk
- matches = M.lookup adlerSum f0AdlerTable >>
- M.lookup (blockSig blk) f0MD4Table
- in
- case matches of
- Just idxs -> do
- is <- go blks
- return $ RBlk (head idxs) : is
- Nothing -> do
- put adlerSum
- is <- go (BL.tail (blk `mappend` blks))
- return $ RChar (BL.head blk) : is
+ sig0 = weakSig $ BL.take (fromIntegral blockSize) fnew
+ go :: Integer -> BL.ByteString -> State Adler32checksum [Instruction]
+ go startIdx fnew | fnew == BL.empty = return []
+ | otherwise = do
+ let (blk, blks) = BL.splitAt (fromIntegral blockSize) fnew
+ endIdx = startIdx + fromIntegral (BL.length blk) - 1
+ adlerSum <- get
+ let matches = M.lookup adlerSum f0AdlerTable >>
+ M.lookup (blockSig blk) f0MD4Table
+ case matches of
+ Just idxs -> do
+ -- modify (`adler32Update` blk)
+ put $ rollingChecksum (fromIntegral startIdx) (fromIntegral endIdx) fnew
+ is <- go (endIdx + 1) blks
+ return $ RBlk (head idxs) : is
+ Nothing -> do
+ let c = BL.head blk
+ c' = BL.head blk -- FIX (should have been blks)
+ -- modify (`adler32Update` BL.singleton c)
+ put $ rollingChecksumUpdate adlerSum c c' startIdx endIdx
+ is <- go (startIdx + 1) (BL.tail (blk `mappend` blks))
+ return $ RChar c : is
f0AdlerTable = toAdlerMap f0sigs
f0MD4Table = toMD4Map f0sigs
RBlk i -> (f0blocks !! i) `mappend` go f0blocks insts
RChar w -> BL.singleton w `mappend` go f0blocks insts
+rollingChecksum :: BL.ByteString -> Int -> Int -> Checksum
+rollingChecksum bs strtIdx endIdx = (csval, strtIdx, endIdx)
+ where csval = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` size
+ buffer = map fromIntegral $ take (endIdx - strtIdx) $ drop strtIdx $ BL.unpack bs
+ indices = map fromIntegral [1..(endIdx - strtIdx + 1)]
+ a = sum buffer
+ b = sum $ zipWith (*) (reverse indices) buffer
+ m = 2^size
+ size = 16
+
+-- given the checksum a(k, l) and b(k, l), find checksum a(k+1, l+1), b(k+1, l+1)
+rollingChecksumUpdate :: Checksum -> BL.ByteString -> Checksum
+rollingChecksumUpdate curCheckSum bs = (csval, oldStrtIdx + 1, oldEndIdx + 1)
+ where (oldChecksum, oldStrtIdx, oldEndIdx) = curCheckSum
+ csval = a `mod` m + ((fromIntegral b) `mod` m) `shiftL` size
+ m = 2^size
+ size = 16
+ bold = oldChecksum `shiftR` size
+ aold = oldChecksum .&. (m - 1)
+ xk = head $ drop oldStrtIdx $ BL.unpack bs
+ xlPlus1 = head $ drop (oldEndIdx + 1) $BL.unpack bs
+ a = aold - fromIntegral xk + fromIntegral xlPlus1
+ b = a + bold - (fromIntegral (oldEndIdx - oldStrtIdx + 1))